Not Applicable
Not Applicable
1. Technical Field
This invention relates in general to communications and, more particularly, to pseudo-random noise sequence generating system.
2. Description of the Related Art
Present code division multiple access (CDMA) systems are characterized by simultaneous transmission of different data signals over a common channel by assigning each signal a unique code. This unique code is matched with a code of a selected receiver to determine the proper recipient of a data signal. Base stations in adjacent cells or transmit areas also have a unique pseudorandom noise (PN) code associated with transmitted data. This PN code is typically generated by a linear feedback shift register (LFSR), also known as a linear sequence shift register (LSSR), and enables mobile stations within the cell to distinguish between intended signals and interference signals. Identification of a PN code requires that the mobile station correctly identify an arbitrary part of the received PN sequence. The identification is frequently accomplished by a correlation of a locally generated PN sequence with the PN sequence received from the base station. The sliding window algorithm often requires the mobile station to efficiently calculate multiple offsets from the LFSR to match the received sequence.
Therefore, a need has arisen for a circuit that can quickly generate multiple offsets in a PN sequence without complex circuitry.
In the present invention, a pseudorandom noise sequence generator is provided with circuitry for generating multiple PN sequences in parallel and circuitry for individually setting offsets between said multiple PN sequences in real time.
The present invention provides significant advantages over the prior art. First, multiple PN sequences with different offsets (relative or absolute) can be generated with respect to a reference system time in a manner of centralized control in applications such as IS-95A/B and/or WCDMA systems. In addition, zero-insertion is supported for lengthening PN sequences by one, which is a requirement for IS-95 standards. In WCDMA (Wide CDMA), the PN generating system can be used for generation of Gold sequences and Kasami sequences. Thus, a single system can support multiple standards.